Phospholipids provide the matrix of all biological membranes, and their metabolic degradation, transportation[unreadable] and participation in membrane remodeling occur.in micelles. In order to elucidate the mechanisms of these[unreadable] processes and to facilitate the use of phospholipid containing micelles as reaction media their structure and[unreadable] physical properties must be delineated. The long term goal of the proposed research is to develop wellcharacterized[unreadable] micellar substrates for the study of lipolytic enzymes. Phospholipases are involved in[unreadable] metabolic degradation of phospholipids; they also participate in vitally important physiological processes[unreadable] including signal transduction, platelet aggregation, cardiac contraction and excitation, and prostaglandin[unreadable] biosynthesis. In these events water soluble lipolytic enzymes act on water insoluble substrates that are[unreadable] organized in supramolecular aggregates (e.g., mixed micelles). Elucidation of the physicochemical properties[unreadable] of the lipid-water interface and its effect on phospholipase catalysis will advance the level of understanding[unreadable] the mechanism of action of these enzymes.[unreadable] The working hypothesis is that by delineating the contributions of the micellar components to the[unreadable] physicochemical properties of the lipid-water interface one will be able to design micelles with targeted[unreadable] physicochemical properties. To test this hypothesis a newly developed spin exchange EPR technique will be[unreadable] used in conjunction with time-resolved fluorescence quenching measurements. 1) Site directed spin[unreadable] labelings, and fluorescent reporter groups will be used to determine the contribution of the alkyl chain to the[unreadable] properties of the micelle, 2) the physicochemical parameters of the polar shell will be determined using the[unreadable] spin probe di-tert.-butyl nitroxide (DTBN), 3) inter-phase solute exchange between the micelles and water[unreadable] will be measured by spin label partitioning, and 4) the relationship between the properties of the lipid-water[unreadable] interface and the rate of phospholipid hydrolysis will be established using a series of secretory[unreadable] phospholipase enzymes. Should the new EPR method prove to be successful in characterizing the mixed[unreadable] micelles here studied, it will open the possibility to apply it to other more complicated supramolecular[unreadable] assemblies (e.g. phospholipids-bile salt mixed micelles) and may become a general technique to[unreadable] characterize micellar aggregates.[unreadable] Relevance to Public Health: Micelles play an important role in biological processes, including drug delivery[unreadable] and membrane function. Elucidation of their structure and properties will provide useful information toward[unreadable] better understanding of membrane-dependent normal and pathological cell functions including cell signaling,[unreadable] inflammation, allergy, apoptosis, as well as membrane fusion.